A Promising Option for Increasing Homicide Clearance Rates

Clearance rates for criminal investigations, particularly for homicides, are a reflection of police performance and a prominent component of offense deterrence. When offenders are not apprehended, the potential deterrent effect of sanctions is diminished and police legitimacy undermined. Clearance rates for serious crimes in the United States have remained essentially unchanged over the last four decades despite decreases in the index crime rate (and more recently, increases in the homicide rate specifically). Moreover, this is surprising considering how technology has advanced during this time. Data from the Uniform Crime Report shows that the nationwide homicide clearance rate decreased from approximately 83% in 1965 to 61% in 2007. It has stabilized in the last decade, with most recent estimates showing 62% in 2018. Hypothesized reasons for declines in clearance rates include an increase in the proportion of homicides involving strangers (e.g. gang- and drug-related violence as opposed to intimate relationship violence), declining societal support for police efforts, and increased regulation of police practices.

It should be emphasized that having a high clearance rate can be helpful in preventing future crime. First, higher clearance rates increase certainty that one will get caught for a crime, which enhances the deterrent effect of related sanctions. Second, if someone is apprehended and imprisoned for a crime, this prevents their ability to commit future crime via incapacitation. Unsolved shootings and homicides in particular feed cycles of gun violence. For example, homicides tend to be concentrated in disadvantaged neighborhoods, where people are more likely to have cynical attitudes toward police and view them as unresponsive. In these neighborhoods, unsolved shootings contribute to the belief that police ‘don’t care,’ and trust in the police erodes. Subsequently, people are less willing to share information on suspected shooters. They also might be more likely to engage in retaliatory violence rather than involving the police should they find themselves in danger. This is particularly true when it comes to people involved in gangs or the illegal drug trade.

Surely, there are factors outside of police control that affect the probability that a case is cleared, such as neighborhood context, whether the shooting occurred outdoors or indoors, the presence of witnesses, and amount of forensic evidence available. For example, recovery of a murder weapon and/or bullets and bullet fragments at the scene improves the likelihood that the case will be solved. Similarly, the presence of DNA evidence at the scene can increase the probability of identifying a suspect. However, it is up to the police officers and investigators to carefully secure and preserve all elements of the crime scene, carefully collect forensic evidence, and follow-up on any leads as soon as possible. Historically, the first 48 hours following the incident are the most critical for investigations.

An investigator’s role is loosely regulated based on how the agency conducts investigations and how its efforts are organized. Some agencies enforce clear requirements for homicide investigations while others have no oversight process at all. For example, some agencies require that specialized forensic technicians respond to homicide scenes along with detectives to better process evidence. Other things that a department can emphasize include things as simple as rapid response time, the importance of carefully and comprehensively securing the scene, and the importance of conducting certain follow-up activities. Follow-up activities happen after the incident, and include things like substantiating witness statements, locating additional witnesses, collecting CCTV footage from neighboring homes, and reviewing mobile phone data.

Research shows that cooperation and engagement with witnesses is key in solving homicide cases, as is the amount of forensic evidence available for collection and analysis. Some of the strongest evidence for this was found in a study in the Boston Police Department (BPD) conducted after the city implemented a problem-oriented policing intervention that sought to improve homicide clearance rates. After experiencing several years of clearance rates below the national average, BPD assigned an advisory committee of sworn and civilian staff members to collaborate with researchers from Northeastern University. The team analyzed BPD’s homicide investigation files, identified best practices, and developed new policies to improve clearance outcomes.

After extensive analysis and consideration, BPD implemented a series of reforms beginning in 2012:

– Additional personnel were assigned to the homicide unit, consisting of a civilian crime analyst, a victim witness resource officer, and eight additional detectives (split across eight squads).

– The homicide unit, Crime Scene Response Unit, and Forensic Group received extensive additional training. Specifically, BPD updated and improved the annual 40-hour crime scene response and investigation in-service training for homicide unit and district detectives. The annual in-service training for Forensic Group and Crime Scene Response Unit was also updated and expanded. Homicide unit detectives attended two supplemental training sessions held at the Boston University medical center and the New York State Homicide Seminar, while two Bureau of Investigative Services deputy superintendents attended the UK National Policing Improvement Agency’s senior investigative officer training.

– BPD implemented a comprehensive set of standardized protocols to guide forensic review activities and reduce variation in practices across individuals. Standardization protocols included the addition of a formal crime scene entry log, formalized witness identification and management techniques, increased deployment of the forensic group to homicide scenes, and consistent collection and storage of evidence, among others.

– To increase accountability in investigations, the BPD homicide unit convened monthly peer review sessions for all open investigations for district detectives and the Forensic Group. Researchers also conducted a rigorous process evaluation to determine the department’s adherence to said policy recommendations, finding significant increases in staffing levels and substantive changes in techniques was implemented successfully.

The BPD evaluation presented compelling evidence that agency policy and individual investigator actions can significantly impact the likelihood of clearing cases, independent of circumstances outside of police control. Researchers compared clearance rates in Boston for the period following the intervention (2012-2014) to the years immediately preceding the intervention (2007-2011). The Boston Homicide Unit experienced a statistically significant 9.8% increase in homicide clearance rates following the intervention, from 47.1% in the period preceding the intervention (2007-2011), to a post-intervention rate of 56.9% (2012-2014). When adjusting for pending cases (i.e., those awaiting grand jury indictment decisions), the post-intervention clearance rate might be as high as 66.2%, indicating an 18.4% increase. When controlling for characteristics outside of police control, such as demographics and location, researchers found a statistically significant 43.4% increase in the odds of clearing an individual homicide case following the intervention. The increase in clearance rates held across case type, including particularly challenging circumstances such as gang- and drug-related cases.

Further, the results suggested the improvements to homicide clearance by BPD were not part of a larger regional or national trend. While BPD’s clearance rate increased by 9.8% following the intervention, the aggregate clearance rate for all other police departments in Massachusetts decreased by 14.9%. Similarly, the aggregate clearance rate in the United States as a whole stayed relatively stable, decreasing by 0.5%. Compared to the aggregate decrease in the rest of Massachusetts and the nationwide stagnation in clearance rates during the same time period, BPD’s significant improvement is noteworthy. Regarding the findings, researchers noted that the particular policy choices in Boston may be less important than the process of determining and adopting best practices. To account for differing regional factors and ensure adoption of policy changes, other agencies seeking to replicate BPD’s results are advised to undertake a similar process of identifying best practices. Evidence from the Boston intervention demonstrates that improvements in criminal investigation techniques and policies can be an effective use of agency resources.

The results from the Boston study were recently highlighted again in a report by the Manhattan Institute regarding whether similar efforts could be used to address New York City’s recent increase in gun crime and homicides. The report also discusses why it is important to clear nonfatal shootings as well as fatal shootings to target gun violence. In theory, solving nonfatal shooting cases might deter shootings in general and/or incapacitate dangerous people before they are able to fatally shoot someone. When researchers compared nonfatal shootings to fatal shootings, both types of incidents had fairly similar case characteristics (sans the fatal injury), indicating that the people committing these crimes were likely similar in nature. One key difference between nonfatal and fatal shooting investigations, though, is that homicides received more sustained investigative efforts during the initial 48 hour period following the incident. This appeared to have an impact on the cooperation of witnesses and the amount of forensic evidence collected and analyzed, which was correlated with the increased clearance rates.

Similar improvements in homicide clearance rates were seen in a study conducted in the Rochester, NY police department (RPD) following changes to the city’s homicide investigation unit. Prior to 2012, the homicide unit was comprised of two sergeants who each supervised four to six investigators. A team of two investigators and a sergeant rotated being “on-call” each week; that team team was assigned to all homicides that occurred during their on-call week. Should more than one homicide occur in that week, the team would occasionally have to drop a case during the initial 48 hours to focus on another homicide. When a homicide would occur, the team would respond, be debriefed by patrol command, and then take over all investigative tasks for the case. There was little supervisory oversight regarding what was done or not done as part of the investigation.

From 2012-2013 RPD implemented many changes to their homicide investigative practices:

-The homicide unit gained additional personnel. Three investigators were added specifically to the homicide unit, and four investigators were added to other units who assisted homicide investigations as needed. Additional personnel assisted in completing critical but time-consuming tasks, such as writing search warrants (e.g. for homes/vehicles, social media, or mobile phone data), retrieving video from neighbors and/or establishments (particularly in a timely manner before data is deleted), and interviewing witnesses.

-The homicide unit was re-organized and included three sergeants who each managed four investigators. Similar to the pre-2012 framework, a team of two investigators and a sergeant rotated being “on-call” each week, and were required to respond to all homicides that occurred during their on-call week. This time though, the sergeant had discretion to call in additional team members to assist in the investigation as needed.

-RPD increased supervisory oversight of homicide investigations through regular progress meetings. Meetings included the team assigned to an investigation, their supervisory captain and lieutenant, personnel from the District Attorney’s office, and representatives from the county crime lab. In addition, lab meetings were to be conducted regularly to review evidence for testing.

-RPD invested in a ‘command vehicle’ that responded to every crime scene. The vehicle, which is essentially an RV, includes a conference room complete with video and internet capabilities. Immediately after a homicide is reported, briefings are held in the command vehicle and tasks can be assigned.

RPD’s enhancements in the homicide unit appeared to have an effect on homicide clearance. 132 homicides were investigated by the homicide unit over 4 years consisting of the pre-intervention period (January 2010-December 2011) and post-intervention period (January 2013-December 2014), and a total of 68% of these cases were solved. The number of murders per year remained somewhat consistent from pre- to post-intervention (34 murders per year compared with 32, respectively). The authors found that investigation tactics did significantly affect the odds of clearance, even after controlling for other theoretically relevant variables (e.g. victim, event, investigator, neighborhood). Homicide clearance rates (i.e., arrest rates) increased by 29% when comparing the pre-intervention period with the post-intervention period, from 54% to 83%. In addition, the average days-to-clearance decreased from pre-intervention to post-intervention, from 75 days to 44 days.

Importantly, some factors outside of police control still remained relevant in clearing homicides regardless of investigation quality. Incidents carried out in a face-to-face manner, in the victim’s and/or offender’s residence, and those involving weapons other than firearms were more likely to be cleared. While these incident characteristics had an independent impact on the case outcome, investigative tactics still exerted an additional effect on homicide clearance rates. The findings support previous research that adequate staffing with competent, well-trained investigators, proper oversight by management, and the immediacy in which tasks are distributed are important covariates in homicide clearance, even in the most difficult of cases. Obviously the chances of clearance will be the greatest when certain incident characteristics are present and a high quality investigation is done, but a high quality investigation will increase the chances of clearance nonetheless.

In addition to strengthening shooting investigations, police agencies can consider complementary strategies to bolster their efforts, such as community problem-solving, hot spots policing tactics, or other problem-oriented policing approaches. As noted in the previously mentioned Manhattan Institute report, the NYPD demonstrated one form of this when it increased the size of its Gun Violence Suppression Division by more than one-third (from 206 to 274 officers). This change was largely in response to recent increases in gun violence and relatedly, a need to improve shooting investigations. The detective work conducted by the gun division is helpful in its own right, but it also serves as a complement to existing homicide units. Officers in the gun violence unit follow similar steps that homicide investigators would, e.g. canvass a neighborhood, interview witnesses and victims, and collect/preserve evidence.

Another example of a gun violence problem-oriented policing intervention is one implemented in the Newark, New Jersey police department (NPD). Gun violence was identified as the primary issue, and crimes related to gun violence largely consisted of homicides, aggravated assaults, and armed robberies. The NPD task force leveraged place-based approaches and conducted meet-and-greets with business managers in target areas (i.e., ‘hot spots’) with the goal of increasing police presence and subsequently preventing gun violence in target areas. There was one police lieutenant who oversaw the field operations each day and used this information to strategically inform operations for the next day. The strategy generated a 35% reduction in gun violence in the target areas relative to the control areas. Even within target areas, the impact on crime varied somewhat throughout the area, decreasing in some spots more than others. In other words, the intervention appeared to decrease crime overall, but especially so in ‘high-risk segments’ that were identified within the target areas. The results are consistent with other research suggesting that consistent and thoughtful implementation of place-based policing strategies can result in crime reduction at those locations. However, there is always the possibility that crime is being displaced to an adjacent area, and this is something that investigators and researchers should continue to monitor when implementing these strategies. It is possible to prevent displacement effects, but careful and thoughtful implementation is key.

Ultimately, there are many factors within police control that can reduce future crime, ranging from targeted police strategies aimed at violence prevention (e.g., problem-oriented policing models) to investigative tactics that increase clearance rates and subsequently prevent violent crime (via deterrence or incapacitation).